Fuel injection valves for gasoline fuel injection systems for internal combustion engines usually operate at comparatively low injection pressure, since the fuel is injected into the induction pipe at a location behind the throttle of the internal combustion engine, so that some vacuum will be available when the engine operates. Such systems require, however, excellent distribution of the fuel within the air stream arising in the induction pipe, that is, essentially complete atomization, so that the atomized drops of fuel will be carried along by the air drawn in during the suction stroke by the pistons of the internal combustion (IC) engine and, additionally, will be uniformly supplied to the various cylinders even if the induction pipe is subdivided downstream of the injection point into branch pipes leading to the respective cylinders. To provide for atomization, it has been proposed to so construct the valve that it is formed with a swirl chamber adjacent the nozzle opening of the valve so that the fuel is sprayed into the induction pipe, operating as a plenum in a form which provides for atomization. This is particularly important in systems in which the injection pulses are short.
A swirling fuel path of fuel within the valve has been obtained by forming the valve in such a manner that fuel is continuously supplied and, unless sprayed into the injection plenum, it can flow back or drain to the source. This permits retention of swirling or rotary motion of the fuel in a centrifugal path within the swirl chamber. It has been found, however, that the accurate proportioning of fuel being injected suffers in such systems because the quantity of fuel being supplied and fuel draining changes when the injection valve opens or closes. Due to the small dimensions of the injection valves it is difficult to so shape the valves that the overall fuel flow is large with respect to the fuel being injected, and thus inaccuracies in the quantity of the fuel being injected have been observed.